JP2017214461A - Inkjet recording ink, inkjet recording method and inkjet recording device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inkjet recording ink capable of effectively suppressing ink clogging, exhibiting excellent discharge stability and having good waterproofness, even in a thermal-system inkjet recording device having a line-type head.SOLUTION: An inkjet recording ink at least includes a pigment, a phthalocyanine compound, water, and a water-soluble compound. The pigment is a resin dispersion pigment including a carbon black dispersed with a (meth)acrylic ester-based random copolymer having an acid number of 100-160 mgKOH/g, inclusive. The phthalocyanine compound has a structure expressed by a general formula (I).SELECTED DRAWING: None

Description

  The present invention relates to an ink for ink jet recording, an ink jet recording method using the ink, and an ink jet recording apparatus. The present invention particularly relates to an ink-jet recording technique using carbon black as a color material suitable for thermal ink-jet recording. In particular, the present invention relates to an ink for inkjet recording that is useful when applied to a long head used in a line system.

  The ink jet recording apparatus has advantages such as low noise, low running cost, easy downsizing of the apparatus, and easy small color full color recording. For this reason, the ink jet recording apparatus is widely applied not only to printers but also to copying machines, printing machines, and the like, and its use is wide-ranging for home use, office use, and industrial use.

  As a recording method of the ink jet recording apparatus, there are a thermal method and a piezo method. Among them, the thermal method in which bubbles are generated in the ink in the nozzles by heating and the ink is ejected has the advantage that the head structure is relatively simple, the recording speed can be increased, and the recording pixels can be increased in density.

  The structure of an ink jet recording head (also referred to as “recording head” or simply “head”) has also evolved. In addition to the conventional serial system that sends and records paper while reciprocating the head left and right, a long head that corresponds to the paper width is used, and the line is used to send only paper without moving the head. The method has been adopted. The line method is suitable for high-speed recording because a sheet can be sent under a fixed long head and recording can be performed at once. Other rain and line systems are being adopted in the fields of large format printers and industrial printers that require high image quality and high speed recording.

  Ink coloring materials that use pigments have become mainstream from the viewpoint of the weather resistance and water resistance of recorded matter. In general, compared with ink using a dye, an ink using a pigment has a clogged nozzle. In particular, when recording is performed with a thermal type line head, there is a demand for an ink that does not clog the nozzles and has excellent ejection stability. On the other hand, improvement of the dispersion stability of pigments using a dispersion resin, a surfactant or the like has been studied. For example, JP-A-2015-183161 and JP-A-2006-342294 propose using a (meth) acrylic ester copolymer as a polymer dispersant (Patent Document 1 and Patent Document 2). reference).

Japanese Patent Laying-Open No. 2015-183161 JP 2006-342294 A Japanese Patent No. 4956717 JP2013-014111A

  The (meth) acrylic acid ester copolymer, which is a polymer dispersant, is suitable for the ink of a thermal ink jet recording apparatus with heat application because of its excellent heat resistance. Moreover, it is preferable to use a (meth) acrylic acid ester random copolymer from the viewpoint of water resistance of the recorded matter.

  However, when ink using a (meth) acrylic acid ester random copolymer is ejected by a thermal line-type head, there is a problem that the nozzle is likely to be clogged. In other words, the discharge stability of the (meth) acrylic acid ester random copolymer is low. Therefore, an object of the present invention is to improve ejection stability with an ink using a (meth) acrylic acid ester-based random copolymer.

  The above object is achieved by an ink jet recording ink, an ink jet recording method, and an ink jet recording apparatus of the present invention having the following configurations.

[1] Ink for ink jet recording The present invention relates to an ink for ink jet recording containing at least a pigment, a phthalocyanine compound, water, and a water-soluble compound, wherein the pigment is an acid of 100 mgKOH / g or more and 160 mgKOH / g or less. A resin-dispersed pigment containing carbon black dispersed by a (meth) acrylic acid ester random copolymer having a valence, wherein the phthalocyanine compound has the general formula (I)

(In the formula, l and m each represent an integer from 0 to 5, n represents an integer from 1 to 5, and l + m + n = 2 to 5).
And a mass ratio of the resin dispersed pigment to the phthalocyanine compound is 1.5: 1 to 6: 1.

  Furthermore, the (meth) acrylic acid ester random copolymer may be a random copolymer of 2-hydroxyethyl methacrylate, methacrylic acid, styrene, benzyl methacrylate, and glycidyl methacrylate. preferable.

[2] Inkjet recording method The present invention is an inkjet recording method for performing recording by ejecting ink from a nozzle array by a thermal method, wherein the nozzle array has a plurality of nozzles, and each of the nozzles is 100 μm ² or more. There is provided an ink jet recording method having an opening area of 350 μm ² or less, wherein the ink is the ink for ink jet recording described in [1]. Here, it is desirable that the total number of nozzles per nozzle row is 1200 or more, and the length of the nozzle row is 5.08 cm (2 inches) or more.

[3] Inkjet recording apparatus The present invention is an inkjet recording apparatus including an ink storage portion and a recording head, wherein the ink storage portion stores the ink for inkjet recording described in [1], and the recording head includes An inkjet recording apparatus is provided that is an inkjet recording head that ejects ink from a nozzle array by a thermal method.

  According to the present invention, clogging of ink is suppressed by using carbon black dispersed by a (meth) acrylic ester random copolymer and a phthalocyanine compound represented by the following general formula (I). , Ejection stability is improved.

FIG. 2 is a diagram schematically illustrating an internal structure of a nozzle of a recording head, (a) is a top view schematically illustrating the internal structure of the nozzle, and (b) is a side view schematically illustrating the internal structure of the nozzle. It is sectional drawing, (c) is a front view which shows an ink discharge outlet typically. FIG. 2 is a diagram schematically illustrating a recording head of the present invention, (a) is a front view schematically illustrating the recording head, (b) is a cross-sectional view taken along a cutting line IIb-IIb, ) Is a cross-sectional view taken along section line IIc-IIc. 1 is a schematic configuration diagram schematically illustrating an overall configuration of an ink jet recording apparatus. It is a block block diagram which shows the control system of the inkjet recording device shown in FIG. 6 is a flowchart showing a recording head recovery sequence process. It is an expanded sectional view of an ink tank. FIG. 3 is an enlarged cross-sectional view of a recording head. FIG. 8 is a diagram illustrating an ink holding member in the recording head illustrated in FIG. 7, (a) is an enlarged perspective view of the ink holding member, and (b) is a cross-sectional view taken along a cutting line VIIIb-VIIIb.

  Hereinafter, the present invention will be described in detail with reference to preferred embodiments of the present invention. However, the present invention is not limited to the following embodiments, and includes all objects having the invention-specific matters.

[1] Ink for ink jet recording The ink for ink jet recording of the present invention contains carbon black, a phthalocyanine compound represented by the general formula (I), water, and a water soluble compound. The ink for inkjet recording of the present invention may contain a surfactant, other solvents, additives and the like as necessary. Hereinafter, it demonstrates for every component.

[1-2] Coloring material The coloring material of the ink of the present invention is obtained by dispersing a pigment in an aqueous medium. The color material is of a type called pigment-resin dispersion (resin dispersion pigment). Among them, the coloring material is obtained by dispersing, in an aqueous medium, a pigment adsorbed with a (meth) acrylic acid ester random copolymer having an acid value of 100 mgKOH / g or more and 160 mgKOH / g or less. The coloring material can be formed by a method known in the prior art such as the method disclosed in Japanese Patent No. 49596917 (see Patent Document 3).

[1-2A] Pigment Carbon black is used as the pigment according to the present invention.

Non-limiting examples of carbon black include furnace black, lamp black, acetylene black, channel black, and the like. For example, commercially available carbon black can be used under the following trade names: Ray Van (available from Aditya Birla Group); Black Pearls L, Legal, Mogul L, Monac ( Monarch, Valcan (from Cabot Corporation); Color Black, Printex, Special Black (from Evonik Industries); and Mitsubishi Carbon Black (from Mitsubishi Chemical Corporation). Of course, the carbon black used in the present invention is not limited to these, and a conventionally known carbon black can also be used. The carbon black used in the present invention has a primary particle size of 10 nm to 40 nm, a BET specific surface area of 50 to 400 m ² / g, a DBP oil absorption of 40 to 200 ml / 100 g, and a volatile content of 0.5 to 10%. , Preferably having a pH of 2-9. Carbon black having the above-described properties is effective for realizing the effects of the present invention. The DBP oil absorption is measured by the A method of JIS K6221: 1982.

[1-2B] Resin Functioning as a Dispersant In the ink of the present invention, a resin-dispersed pigment dispersed with a (meth) acrylic acid ester-based copolymer is used as a color material. In the present invention, a (meth) acrylic ester copolymer that is more preferable from the viewpoint of dischargeability is used as a dispersant. The (meth) acrylic acid ester copolymer used in the present invention is obtained by copolymerizing (meth) acrylic acid, (meth) acrylic acid ester, and a monoethylenically unsaturated monomer copolymerizable therewith. Can be obtained. The (meth) acrylic acid ester copolymer includes a random copolymer, a block copolymer, a graft copolymer, and the like. In the present invention, a random copolymer is used. This is because many of the copolymers (for example, block copolymers) other than the random copolymer have another problem of increasing the hydrophilicity of the resin-dispersed pigment and decreasing the water resistance of the recorded image.

[1-2B-1] Monomer component for producing resin (Meth) acrylic acid contains acrylic acid and methacrylic acid. Considering that the coexistence range of the electrical neutral state and the anion state can be widely controlled, availability, price, etc., it is preferable to use methacrylic acid.

Non-limiting examples of (meth) acrylic esters are:
Methyl (meth) acrylate, n-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, dodecyl (meth) acrylate, octadecyl (meth) acrylate, cyclohexyl (meth) acrylate, isobornyl ( Alkyl (meth) acrylates such as (meth) acrylate;
Hydroxyalkyl (meth) acrylates such as 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate;
Diethylene glycol mono (meth) acrylate, triethylene glycol mono (meth) acrylate, polyethylene glycol mono (meth) acrylate, propylene glycol mono (meth) acrylate, dipropylene glycol mono (meth) acrylate, tripropylene glycol mono (meth) acrylate, Tetramethylene ether glycol mono (meth) acrylate, polyethylene oxide-polypropylene oxide random polymer glycol or block polymer glycol mono (meth) acrylate, polyethylene oxide-polytetramethylene ether random polymer glycol or block polymer glycol mono Alkylene glycol mono (meth) acrylates such as (meth) acrylate;
Glycidyl (meth) acrylate;
Including benzyl (meth) acrylate.

  The (meth) acrylic acid ester copolymer used in the ink of the present invention is a styrene-based monomer in addition to the aforementioned (meth) acrylic acid, (meth) acrylic acid ester, monoethylenically unsaturated monomer. The body can be included. Non-limiting examples of the styrene monomer are styrene, α-methyl styrene, 2-methyl styrene, 3-methyl styrene, 4-methyl styrene, 4-t-butyl styrene, 4-methoxy styrene, 4 -Including chlorostyrene. That is, the above-mentioned (meth) acrylic acid ester copolymer is preferably a styrene- (meth) acrylic acid copolymer having a styrene monomer.

[1-2B-2] Resin Characteristics The (meth) acrylic acid ester copolymer used in the ink of the present invention has an acid value of 100 mgKOH / g or more and 160 mgKOH / g or less. By having an acid value within the above-mentioned range, the hydrophilicity of the pigment is controlled to prevent the occurrence of bleeding of the recorded matter due to the elution of the pigment due to adhesion of water or the like, and in the thermal type inkjet recording apparatus Good ejection stability can be maintained. More preferably, the (meth) acrylic acid ester-based copolymer has an acid value of 110 mgKOH / g or more and 150 mgKOH / g. The acid value means the amount (mg) of KOH required to neutralize 1 g of resin, and is useful as an index indicating the hydrophilicity of the resin. The acid value can also be obtained by calculation from the composition ratio of monomers constituting the resin. Alternatively, when the composition ratio of the monomer is unknown, the acid value of the resin dispersed pigment can be measured by potentiometric titration using a potentiometer such as Titrino (manufactured by Metrohm AG).

  The weight average molecular weight (Mw) of the (meth) acrylic acid ester copolymer used in the ink of the present invention can be measured by a gel permeation chromatography (GPC) method. The (meth) acrylic acid ester copolymer used in the ink of the present invention preferably has a Mw in the range of 6,000 to 12,000, more preferably 7,000 to 9,000 in terms of polystyrene. . By having Mw within the range of 6,000 to 12,000, the dispersion stability of the resin-dispersed pigment can be increased, the viscosity can be set low, and the phenomenon that the pigment adheres to the heater portion (kogation) is prevented. A stable recording can be performed for a period of time.

[1-2B-3] Amount of Resin with respect to Pigment In the ink of the present invention, it is desirable to adjust the mass ratio of the (meth) acrylic ester copolymer to the pigment within the range of 0.2 to 1.0. By having a mass ratio within the above-mentioned range, it is possible to maintain the dispersibility of the resin-dispersed pigment and to maintain the ink viscosity low.

[1-2C-1] Resin-dispersed pigment The resin-dispersed pigment used in the ink of the present invention can be prepared, for example, by coating the pigment with a (meth) acrylic ester random copolymer. The average particle size of the resin-dispersed pigment used in the present invention is preferably in the range of 70 nm to 150 nm, more preferably 80 nm to 120 nm. By having an average particle diameter within the above range, the dispersion stability of the resin-dispersed pigment is maintained over a long period of time, and sufficient color developability is imparted to the resin-dispersed pigment to form an image. Sufficient weather resistance can be imparted to the image. The average particle diameter can be measured by a dynamic light scattering method in a liquid. For measurement of the average particle size, laser light such as FPAR-1000 (Otsuka Electronics Co., Ltd., cumulant method analysis), Nanotrack UPA 150EX (Nikkiso Co., Ltd., 50% integrated value) is used. A particle size distribution measuring device can be used.

  The concentration of the resin-dispersed pigment in the inkjet recording ink is preferably 0.5% by mass or more and 10% by mass or less, more preferably 1.0% by mass or more and 8.0% by mass, based on the total mass of the inkjet recording ink. % Or less, more preferably in the range of 1.5% by mass or more and 6.0% by mass or less. By having a concentration within the above range, it is possible to impart sufficient color developability to the inkjet recording ink to form an image and to suppress stable increase in viscosity of the inkjet recording ink, thereby enabling stable ejection. Can do.

[1-2C-2] Production Method The resin-dispersed pigment includes, for example, (a) a step of dissolving a (meth) acrylic acid ester random copolymer in an aqueous solution of a basic substance to obtain a dispersant solution; b) adding a pigment to the dispersant solution, and coating the pigment with a (meth) acrylic acid ester random copolymer. The method described above includes (c) an acid precipitation step of adding an acidic substance to the dispersant solution to which the pigment has been added, (d) a filtration step of separating the obtained precipitate, and (e) a basic substance. It may further include a redispersion step that is used to disperse the precipitate in the aqueous medium.

  In the acid precipitation step (c), the anionic group in the (meth) acrylic acid ester random copolymer generated by neutralization in the step (a) is converted into a non-ionized state before neutralization, A (meth) acrylic ester random copolymer is deposited on the pigment surface. More specifically, in the acid precipitation step (c), hydrochloric acid, sulfuric acid, acetic acid is added to the aqueous dispersion obtained in the concentration step performed as necessary after step (b) or step (b). It can carry out by adding acids, such as. By performing the acid precipitation step (c), the interaction between the pigment and the (meth) acrylate random copolymer can be further increased. As a result, the resin-dispersed pigment exhibits excellent effects in terms of physical properties such as a high level of dispersion and high dispersion stability. In addition, the resin-dispersed pigment exhibits excellent effects in terms of suitability for use, such as a short dispersion time and high solvent resistance.

  In the method including steps (a) to (e), more preferably, (f) the precipitate separated by filtration is washed and not adhered to the pigment between step (d) and step (e). You may implement the washing | cleaning process which removes a (meth) acrylic-ester type random copolymer.

[1-2] Phthalocyanine compound:
The phthalocyanine compound used in the present invention has the general formula (I).

  In formula (I), l and m each represent an integer from 0 to 5, n represents an integer from 1 to 5, and l + m + n = 2 to 5.

  Although details are unknown, the reason why the ejection stability of the ink for ink jet recording is improved when a phthalocyanine compound is added to the resin-dispersed pigment is estimated as follows. The aromatic ring of the phthalocyanine compound of formula (I) can form π-π stacking due to hydrophobic interaction with the aromatic ring of carbon black. Although details are unknown, it is considered that the side chain melamine ring and / or disulfophenyl group also contributes to the promotion of the formation of π-π stacking. Due to the above effect, it is considered that the phthalocyanine compound is adsorbed on the surface of carbon black. Therefore, in the non-adsorbed portion of the (meth) acrylate random copolymer on the surface of the carbon black or the portion where the (meth) acrylate random copolymer is desorbed by the heat during ink ejection, π− The phthalocyanine compound of the formula (I) can be adsorbed by π stacking. As a result, aggregation of carbon black is prevented, and it is considered that ink for inkjet recording can be stably discharged.

  The concentration of the phthalocyanine compound of formula (I) in the inkjet recording ink is preferably 0.1% by mass or more and 5% by mass or less, more preferably 0.1% by mass or more, based on the total mass of the inkjet recording ink. It is within the range of 3% by mass or less. From the viewpoint of improving the dispersion stability, the content of the phthalocyanine compound of the formula (I) in the ink for inkjet recording is preferably set to not more than the content of the pigment. More preferably, the mass ratio of the resin dispersed pigment to the phthalocyanine compound of formula (I) is in the range of 1.5: 1 to 6: 1. By having a mass ratio within the above-mentioned range, it is possible to achieve appropriate dispersion, prevent aggregation of pigments and decrease in water resistance of ink for ink jet recording, and enable stable ejection of ink for ink jet recording. To do.

[1-3] Water-soluble compound The ink for inkjet recording of the present invention contains a water-soluble compound. The total mass of the water-soluble compound is preferably about 50% by mass or less based on the total mass of the ink for inkjet recording. The selection of a water-soluble compound is important in order to adjust the storage stability of the ink for inkjet recording and the moisture retention at the nozzle tip. Non-limiting examples of water-soluble compounds that can be used in the present invention are:
Monools such as ethanol, 1-propanol, 2-propanol, 1-butanol, furfuryl alcohol, tetrahydrofurfuryl alcohol, cyclohexanol, diacetone alcohol;
Ethylene glycol, propylene glycol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 1,5-pentanediol, 2,4-pentanediol, neopentyl Glycol, 1,2-hexanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, 2,5-hexanediol, hexylene glycol (2-methylpentane-2,4-diol), Diols such as 1,4-cyclohexanediol, hexane-2,5-diol, diethylene glycol, triethylene glycol, polyethylene glycol 300, tripropylene glycol, butylene glycol, thiodiglycol;
Polyols such as trimethylolpropane, trimethylolethane, pentaerythritol;
Triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, dipropylene glycol monomethyl ether, ethylene glycol monophenyl ether, triethylene glycol monobutyl ether, tripropylene glycol monomethyl ether, glycerin monoallyl ether, 1-methoxy-2-propanol, Ethers such as triethylene glycol dimethyl ether, triethylene glycol diethyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether;
Ketones such as acetonylacetone;
Sulfones such as sulfolane, dimethyl sulfoxide, bis (2-hydroxyethyl) sulfone;
ureas such as β-dihydroxyethyl urea, urea, ethylene urea, 1,3-dimethyl-2-imidazolidinone;
Amides such as N-methyl-2-pyrrolidone and 2-pyrrolidone;
Including esters such as glycerin monoacetate, glycerin diacetate, glycerin triacetate, and γ-butyrolactone.

  Particularly preferred water soluble compounds include glycerin, triethylene glycol, ethylene urea, trimethylol propane, and bis (2-hydroxyethyl) sulfone.

[1-4] Surfactant:
The ink for inkjet recording of the present invention may further contain one or more kinds of surfactants as necessary. The surfactant controls the surface tension of the ink for ink jet recording, controls the bleeding and penetration of the ink for ink jet recording when attached to the recording medium, and controls the wettability and ejection performance of the ink for ink jet recording in the recording head. It has an effect of improving and / or preventing pigment adhesion to a heater portion in the recording head. The surfactant may be a nonionic surfactant, an anionic surfactant, a cationic surfactant or an amphoteric surfactant. Non-limiting examples of nonionic surfactants include polyoxyethylene alkyl ether, polyoxyethylene fatty acid ester, polyoxyethylene alkylphenyl ether, polyoxyethylene / polyoxypropylene block copolymer, fatty acid diethanolamide, alkyne diol Including derivatives. Non-limiting examples of anionic surfactants include polyoxyethylene alkyl ether sulfate, polyoxyethylene alkyl ether sulfonate, polyoxyethylene alkyl phenyl ether sulfate, polyoxyethylene alkyl phenyl ether sulfonate , Α-sulfo fatty acid ester salts, alkylbenzene sulfonates, alkylphenol sulfonates, alkylnaphthalene sulfonates, alkyltetralin sulfonates, sulfosuccinic acid dialkyl ester salts, and the like. Non-limiting examples of cationic surfactants include alkyl trimethyl ammonium salts, dialkyl dimethyl ammonium chlorides and the like. Non-limiting examples of amphoteric surfactants include alkyl carboxybetaines and the like.

  Particularly preferred surfactants include alkynediol derivatives and polyoxyethylene alkyl ethers.

  Alkynediol derivatives include alkynediol and alkynediol ethylene oxide adducts. Non-limiting examples of alkynediol derivatives include 2,4,7,9-tetramethyl-5-decyne-4,7-diol (compound of formula (II) where u = v = 0) and its ethylene oxide Adducts (compounds of formula (II) where u> 0 and v> 0).

[1-5] Other Additives The ink for inkjet recording of the present invention may contain other additives as necessary. Non-limiting examples of additives include pH adjusters, rust inhibitors, preservatives, antifungal agents, antioxidants, antireducing agents, salts and the like.

[1-6] Water The ink for inkjet recording of the present invention contains water. It is preferable to use deionized water (ion exchange water). The water content in the inkjet recording ink of the present invention is not particularly limited. Typically, the ink for inkjet recording of the present invention is preferably 30% by mass or more and 90% by mass or less, more preferably 40% by mass or more and 85% by mass or less, and most preferably 50% by mass or more and 80% by mass or less. including. By setting the water content to 30% by mass or more, the pigment can be hydrated and the water-soluble compound can be dissolved, and aggregation of the pigment and the water-soluble compound can be prevented. On the other hand, by setting the water content to 90% by mass or less, even when the amount of the water-soluble organic compound is relatively increased and the volatile component (such as water) in the aqueous medium is volatilized, the pigment The dispersion state can be maintained. In other words, precipitation and solidification of the pigment can be prevented by setting the water content to 90% by mass or less.

[1-7] Surface Tension The ink for inkjet recording of the present invention preferably has a surface tension γ of 25 mN / m or more and 45 mN / m or less. By having a surface tension γ of 25 mN / m or more, it is possible to maintain a meniscus at the ink discharge port and to prevent the ink jet recording ink from flowing out from the ink discharge port. Further, by having a surface tension γ of 45 mN / m or less, the absorption speed of the ink into the recording medium can be optimized, and fixing failure due to insufficient absorption of the ink for inkjet recording can be prevented. The surface tension γ of the ink for inkjet recording of the present invention is a platinum plate using an automatic surface tension meter (for example, “CBVP-Z type” manufactured by Kyowa Interface Science Co., Ltd.) under the conditions of a temperature of 25 ° C. and a humidity of 50%. Means the value measured by the plate method using The surface tension γ of the ink for ink jet recording can be adjusted by the kind and addition amount of the surfactant, the kind and addition amount of the water-soluble compound.

[1-8] Viscosity The ink for inkjet recording of the present invention is preferably 1.8 mPa · s to 5.0 mPa · s, more preferably 1.8 mPa · s to 3.5 mPa · s, most preferably 1. It may have a viscosity η of not less than 8 mPa · s and not more than 3.0 mPa · s. By having a viscosity η of 1.8 mPa · s or more, a markedly excellent sedimentation suppressing effect can be obtained. On the other hand, according to the study by the inventors of the present application, although having a viscosity η of 5.0 mPa · s or less, carbon black having an extremely small particle diameter (primary particle diameter of 10 nm or more and 40 nm or less) is used. Good ink storage stability can be obtained.

  The viscosity η of the ink is an E-type viscometer (for example, “RE-80L viscometer” manufactured by Toki Sangyo Co., Ltd.). It shall mean a value measured according to JIS Z 8803: 2011 under the condition of a temperature of 25 ° C. The viscosity η of the ink for inkjet recording of the present invention can be adjusted by the kind and addition amount of the surfactant, the kind and addition amount of the water-soluble compound. The kinematic viscosity ν can be calculated by the equation ν = η / ρ based on the density ρ and the viscosity η. The ink density ρ can be measured by any method known in the art, such as the Archimedes method or the specific gravity bottle method.

[1-9] pH
The ink for inkjet recording of the present invention may have a pH of preferably 6.0 or more and 10.0 or less, more preferably 7.0 or more and 9.5 or less. By having a pH of 6.0 or higher, the dispersion stability of the carbon black used as the pigment can be maintained and aggregation of the pigment can be prevented. On the other hand, by having a pH of 10.0 or less, it is possible to prevent the elution of organic substances and / or inorganic substances from the members of the apparatus in contact with the ink and maintain the ink ejection stability. The pH of the ink for inkjet recording of the present invention means a value measured using a pH meter (for example, “D-51” manufactured by Horiba, Ltd.) at a temperature of 25 ° C.

[2] Recording Head Hereinafter, one embodiment of the recording head of the present invention will be described with reference to the drawings. However, the recording head of the present invention is not limited to the configuration described below.

[2-1] Structure of Nozzle Part First, the structure of the nozzle part will be described with reference to FIG. FIG. 1A is a top view schematically showing the internal structure of the nozzles of the recording head. FIG.1 (b) is sectional drawing which shows typically the internal structure of the nozzle shown to Fig.1 (a). FIG. 1C is a front view schematically showing an ink discharge port of the nozzle shown in FIG.

  As shown in FIG. 1, the thermal recording head is formed with a nozzle row including a plurality of nozzle channels 159 partitioned by nozzle walls 153. Each of the plurality of nozzle channels 159 has an ink ejection port 151 that communicates therewith. Further, a heater 152 for discharging ink is disposed inside each nozzle channel 159. The head having such a structure can cause ink droplets to fly from the ink discharge ports 151 by heating the ink filled in the nozzle flow path 159 with the heater 152 and causing the ink to foam.

  In the form shown in FIG. 1, a nozzle filter 155 for trapping foreign matter floating in the nozzle flow path 159 is installed between the nozzle flow path 159 and the common liquid chamber 112. The top plate member 113 to which the nozzle top plate 162 is attached has an ink supply opening (not shown) formed by anisotropic etching or the like, and introduces external ink from the common liquid chamber 112 to the nozzle flow path 159. It is configured to be possible.

  The nozzle channel 159 has a top surface partitioned by a nozzle top plate 162 and a bottom surface partitioned by a nozzle bottom plate 164 in addition to the right and left side surfaces partitioned by a nozzle wall 153. That is, the nozzle channel 159 is a substantially rectangular columnar internal space separated from the surrounding space by using the nozzle wall 153, the nozzle top plate 162, and the nozzle bottom plate 164 as partition walls. The nozzle top plate 162 is attached to a top plate member 113 made of Si or the like, and the nozzle bottom plate 164 is attached to the heater substrate 111.

The ink discharge port 151 is an opening that is formed at one end of the nozzle channel 159 and discharges ink. The ink discharge port 151 is communicated with the common liquid chamber 112 via the nozzle channel 159. The ink discharge port 151 is formed on the face surface (discharge port forming surface). In the example shown in FIG. 1, the face surface is formed integrally with the nozzle wall 153. However, a face plate (not shown) may be separately installed to form the face surface. The ink discharge port 151 may have an opening area of 100 μm ² or more and 350 μm ² or less. By setting the opening area to 100 μm ² or more, it is possible to prevent the occurrence of undischarge nozzles. On the other hand, by setting the opening area to 350 μm ² or less, it is possible to discharge minute ink droplets having a volume of 10 pL or less. Ink droplets having a volume of 10 pL or less make it possible to achieve a resolution of 600 dpi or more. The opening area is represented by the product of the discharge port width 171 and the discharge port height 172.

  The recording head shown in FIG. 1 is a line type head in which a nozzle row is formed by a plurality of nozzle channels 159. The number of nozzle flow paths 159 forming the nozzle row (that is, the total number of nozzles) is not particularly limited. In order to exhibit the effects of the present invention, it is particularly desirable that the number of nozzle flow paths 159 per nozzle row (that is, the total number of nozzles) be 1200 or more. The total number of nozzles per nozzle row may be preferably 1200 or more and 9600 or less, more preferably 1200 or more and 4800 or less. In addition, the length of the nozzle row is desirably 5.08 cm (2 inches) or more. The length of the nozzle row is preferably 5.08 cm (2 inches) or more and 10.16 cm (4 inches) or less.

  The heater 152 is a heating unit for heating and foaming the ink filled in the nozzle channel 159. The heater 152 is installed on the heater substrate 111. The heater 152 can be formed using, for example, a resistor made of tantalum nitride or the like. The heater 152 is connected to an electrode (not shown) made of aluminum or the like for energization, and a switching transistor (not shown) for controlling the energization to the heater 152 is connected to one end of the electrode. Yes. The drive of the switch transistor is controlled by an IC including a circuit such as a control gate element, and the heater 152 is driven in a predetermined pattern by a signal from the outside of the head.

  The recording head can be driven at a driving frequency of preferably 1 kHz or more and 10 kHz or less. By driving at a driving frequency of 1 kHz or more, even when the amount of ink per droplet is extremely small, the amount of ink applied per unit time can be increased, and the amount of image data and the number of recording dots can be increased. That is, a high-quality image can be recorded at high speed. By driving at a driving frequency of 10 kHz or less, the amount of ink supplied to the nozzles is insufficient compared to the amount of ink discharged, so that ejection stability during high-speed recording can be maintained. In order to obtain the above-described effect more reliably, it is preferable to use a recording head that can be driven at a driving frequency of 3 kHz to 8 kHz. Further, the recording head of the present invention is preferably driven at a driving frequency of 6 kHz or more and 10 kHz or less because a drop in ejection stability and nozzle ejection failure are unlikely to occur even under a high driving frequency.

  The overall length of the nozzle is preferably 200 μm or more and 300 μm or less. In this specification, the “total length of the nozzle” means the length of the nozzle channel 159. Specifically, the “total length of the nozzle” means the length 170 from the end on the ink discharge port 151 side of the nozzle wall 153 constituting the nozzle channel 159 to the end on the common liquid chamber 112 side.

  The nozzle flow path 159 includes a nozzle front portion 181 that is a portion from the heater center 157 to the end portion on the ink discharge port 151 side, and a nozzle rear portion 182 that is a portion from the heater center 157 to the end portion on the common liquid chamber 112 side. It is divided into and. From the viewpoint of the discharge speed, the ratio of the flow resistance (front resistance) of the nozzle front part 181 to the flow resistance (rear resistance) of the nozzle rear part 182 is 0.3 or more and 0.8 or less. It is preferable. The flow resistance can be obtained by calculation according to Hagen-Poiseuille's law from values such as the cross-sectional area of the flow path, the flow path length, and the kinematic viscosity ν of the ejected ink. That is, if the ink to be used (and its kinematic viscosity ν) is determined, the value of the front resistance / rear resistance can be adjusted by the flow path cross-sectional area of the nozzle, the flow path length, and the like.

[2-2] Nozzle Material The nozzle wall 153, the nozzle top plate 162, and the nozzle bottom plate 164 that partition the nozzle flow path 159 can be formed of, for example, a photosensitive resin. The photosensitive resin includes a negative photoresist. Non-limiting examples of commercially available negative photoresists are: “SU-8 series” and “KMPR-1000” (available from Nippon Kayaku Co., Ltd.); and “TMMR”, “TMMR-S2000” and Includes "TMMF-S2000" (Tokyo Ohka Kogyo Co., Ltd.). Among them, it is preferable to use an epoxy photosensitive resin having excellent solvent resistance and excellent strength as a nozzle wall. Commercially available epoxy photosensitive resins include “TMMF-S2000” (manufactured by Tokyo Ohka Kogyo Co., Ltd.).

[2-3] Hydrophilic region and water-repellent region In the recording head used in the present invention, it is preferable to form a hydrophilic region or a water-repellent region on the periphery of the ink discharge port 151. Whether to form a hydrophilic region or a water-repellent region may be determined in consideration of the type of color material contained in the ink jet recording ink to be used, the surface tension γ of the ink jet recording ink, and the like.

For example, when using the inkjet recording ink of the present invention in which the color material is a pigment, a recording head (hydrophilic head) in which a hydrophilic region is formed at the periphery of the ink discharge port 151 is preferable. The hydrophilic region preferably has a contact angle of 60 ° or less, more preferably 0 ° with respect to the ink used. In the present invention, the contact angle of the hydrophilic region or the water repellent region, JIS R3257: conforms to 1999, using a contact angle meter (for example, trade name "SIMAGE-mini", Ltd. excimer Ltd.), tan ^- It can be measured by the ¹ (θ / 2) method. Also in the examples described later, the contact angle is measured by the above method.

  For the hydrophilic area, a method for forming the member (face material) forming the ink discharge port 151 with a hydrophilic material, a method for hydrophilic treatment of the surface of the face material (face surface), and imparting a hydrophilic film to the face surface It can form by the method of doing. The face material can be formed using, for example, a resin such as an epoxy resin, particularly an epoxy photosensitive resin.

Non-limiting examples of hydrophilic treatment of the face surface include roughening of the face surface. Non-limiting examples of roughening include laser irradiation treatment, UV / O ₃ treatment, plasma treatment, heat treatment, oxidation treatment, and embossing treatment. An excimer laser, a YAG laser, a CO ₂ laser, or the like can be used for the laser irradiation treatment. Alternatively, the hydrophilic treatment of the face surface may be performed by immersing the peripheral edge of the ink discharge port 151 in a liquid having high hydrophilicity for a long time. “Liquid with high hydrophilicity” includes pigment ink and the like. For example, the hydrophilic treatment of the face surface can be performed by immersing the face material in the pigment ink to be used for 10 minutes or more.

  Non-limiting examples of the hydrophilic film applied to the face surface include a metal film and a hydrophilic resin film. In addition to high hydrophilicity, it is preferable to form a hydrophilic film using a material having good adhesion to the face material. Non-limiting examples of materials that can be used include compositions comprising water-soluble resins and water-insoluble low molecular weight compounds. For example, a water-soluble resin (such as hydroxypropylcellulose) and a water-insoluble low molecular weight compound (such as bisphenol A) are dissolved in a suitable solvent (such as N, N-dimethylformamide), and the solution is applied to the face surface. A hydrophilic film | membrane can be formed by drying a coating film and processing a dry coating film with alcohol etc. as needed.

The method for forming the hydrophilic region may be appropriately selected from the methods described above according to the material constituting the face material. In addition, the hydrophilic region may be formed by combining two or more of the above methods. One example of a preferred method includes forming a face material using an epoxy-based photosensitive resin, subjecting the face surface to UV / O ₃ treatment, and immersing it in pigment ink.

[2-4] Overall Structure of Recording Head Next, an example of the entire structure of the recording head will be described with reference to FIGS. A recording head having the structure shown in FIGS. 2A to 2C is disclosed in Japanese Patent Laid-Open No. 2013-014111 (see Patent Document 4). Therefore, in this specification, the content of Unexamined-Japanese-Patent No. 2013-014111 is quoted, and only the outline is demonstrated. 2A is a front view schematically showing the recording head, FIG. 2B is a cross-sectional view taken along a cutting line IIb-IIb, and FIG. 2C is a cutting line IIc-IIc. FIG. For convenience of explanation, the liquid supply case cover is omitted in FIG.

  Preferably, the recording head of the present invention is a line type head as shown in FIG. The recording head of this example includes a common liquid chamber 112 that communicates with a plurality of nozzle flow paths that form a nozzle row, a liquid supply port 127 that communicates with the common liquid chamber 112, and a main liquid supply chamber that communicates with the liquid supply port 127. 126 and a liquid supply path 137 communicating with the main liquid supply chamber 126. The recording head of this example communicates with the liquid supply path 137 and is divided into a first liquid supply chamber 134 and a second liquid supply chamber 135 from the upstream side, the first liquid supply chamber 134 and the second liquid. And a supply filter 118 arranged to be separated from the supply chamber 135. The recording head of this example further includes a gas-liquid separation unit 120 provided in a part of the main liquid supply chamber 126 and an air chamber 141 communicating with the gas-liquid separation unit 120.

  A nozzle channel, a common liquid chamber 112, a liquid supply port 127, a main liquid supply chamber 126, a liquid supply path 137, a liquid supply chamber (first liquid supply chamber 134, second liquid supply chamber 135), The supply filter 118, the gas-liquid separator 120, and the air chamber 141 are arranged as shown in FIG. That is, they are preferably arranged on a plane parallel to a plane including the nozzle channel arrangement direction and the liquid discharge direction. Furthermore, it is preferable that the main liquid supply chamber 126, the liquid supply path 137, the supply filter 118, the gas-liquid separator 120, and the air chamber 141 are arranged without being stacked.

  The recording head having the structure shown in FIGS. 2A to 2C is referred to as a gas-liquid separation type recording head. A gas-liquid separation type recording head is difficult to ensure ejection stability as compared with a recording head having a conventional structure. This is because the ink is filled in the nozzle by utilizing the weight of the ink. Therefore, it can be said that the gas-liquid separation type recording head is one of the forms in which the effects of the present invention can be most enjoyed.

  A ceramic base plate 110 supports a heater substrate 111 formed of silicon. The heater substrate 111 is formed with a plurality of electrothermal transducers (heaters) as liquid discharge energy generating elements and a plurality of flow path walls for constituting nozzles corresponding to these electrothermal transducers. Yes. The heater substrate 111 is also formed with a liquid chamber frame surrounding the common liquid chamber 112 communicating with each nozzle. A top plate member 113 that forms the common liquid chamber 112 is joined on the side wall of the nozzle and the liquid chamber frame formed in this manner. Therefore, the heater substrate 111 and the top plate member 113 are laminated and bonded to the base plate 110 in an integrated state. Such lamination adhesion is performed with an adhesive having good thermal conductivity such as silver paste. A mounted electrical wiring board (PCB) 114 is supported by a double-sided tape (not shown) behind the heater board 111 in the base plate 110. Each ejection energy generating element on the heater substrate 111 and the PCB 114 are electrically connected by wire bonding corresponding to each wiring.

  A liquid supply member 115 is joined to the top surface of the top plate member 113. The liquid supply member 115 includes a liquid supply case 116 and a liquid supply case cover 117. The liquid supply case cover 117 closes the upper surface of the liquid supply case 116, thereby forming a liquid chamber and a liquid supply path described later. The liquid supply case 116 and the liquid supply case cover 117 are joined with, for example, a thermosetting adhesive. The liquid supply case 116 is provided with a supply filter 118 and a discharge filter 119. The purpose of the supply filter 118 is to remove foreign substances in the liquid supplied to the liquid supply member 115. The purpose of the discharge filter 119 is to prevent foreign matter from entering from the outside of the recording head. Each of the supply filter 118 and the discharge filter 119 is fixed to the liquid supply case 116 by heat welding. Further, a gas-liquid separator 120 is formed in a part of the liquid supply case 116. In addition, a liquid level detection sensor 121 is mounted from the outside so as to protrude into the gas-liquid separation unit 120, and controls the amount of liquid in the liquid chamber.

  Here, the configuration of the liquid chamber, the liquid supply path, and the like formed by fitting the liquid supply case 116 and the liquid supply case cover 117 will be described. A liquid supply port 127 that is substantially parallel to the nozzle arrangement direction and is a rectangular opening is formed on the joint surface of the liquid supply case 116 with the top plate member 113. Further, on the extension of the liquid supply port 127, a storage liquid main liquid supply chamber 126 is formed. That is, the main liquid supply chamber 126 is formed substantially parallel to the nozzle row and across the width of the nozzle row. Further, the top surface on the side opposite to the liquid supply port 127 constitutes an inclination (main liquid supply chamber inclination 129) with the gas-liquid separation part 120 as the uppermost portion over almost the entire area. Two openings are formed in the main liquid supply chamber inclination 129, one being the liquid communication part 131 and the other being the gas-liquid separation part 120.

  The gas-liquid separator 120 is formed as a part of the main liquid supply chamber 126 and has a depth larger than that of the other parts of the main liquid supply chamber 126. This is to enhance the effect of breaking bubbles that are mixed in the liquid in the liquid chamber, as will be described later. In the form of FIG. 2, three stainless steel electrodes, which are the upper limit detection electrode 123, the ground electrode 124, and the lower limit detection electrode 125, are mounted inside the gas-liquid separation unit 120 from the left side in FIG. Has been. The liquid level in the main liquid supply chamber 126 is between the upper limit and the lower limit depending on the presence / absence of energization between the ground electrode 124 and the upper limit detection electrode 123 and the presence / absence of energization between the ground electrode 124 and the lower limit detection electrode 125. It is the structure which detects whether or not. In the recording head of the form shown in FIG. 2, the detection reliability can be improved by detecting the liquid level of the liquid that has undergone gas-liquid separation.

  An air communication part 130 is provided on the extension of the gas-liquid separation part 120, and an air chamber 141 that functions as an air flow path is provided at the tip of the air communication part 130. A discharge filter 119 communicating with the discharge joint 133 is disposed at the tip of the air chamber 141. The discharge filter 119 is formed of a material having water repellency. If liquid flows into the air flow path (air chamber 141), ink may adhere to the discharge filter 119, and an ink meniscus may be formed inside the discharge filter 119. Even when a meniscus is formed, the ink can be easily removed by reducing the capillary tension of the filter portion by the water repellency of the discharge filter 119.

  On the other hand, a liquid supply path 137 is provided via a liquid communication portion 131 provided in the main liquid supply chamber inclination 129. The liquid supply path 137 has a tubular shape from the liquid communication part 131 to the vicinity of the supply filter 118, and is formed on substantially the same plane as the main liquid supply chamber 126. The supply filter 118 is also disposed on substantially the same plane as the main liquid supply chamber 126. The supply filter 118 is disposed so as to separate the liquid supply chamber into two chambers. A chamber communicating with the supply joint 132, that is, an upstream chamber along the flow of liquid supply in the recording head is a first liquid supply chamber 134, and a downstream chamber is a second liquid supply chamber 135. The supply filter 118 is disposed on substantially the same plane as the main liquid supply chamber 126. Therefore, the first liquid supply chamber 134 and the second liquid supply chamber 135 adjacent to both surfaces of the supply filter 118 are also disposed on substantially the same plane as the main liquid supply chamber 126 and the ink discharge port arrangement surface 139. Become.

  The second liquid supply chamber 135 has an opening (hereinafter referred to as “second liquid supply chamber opening 136”) communicating with the liquid supply path 137 above the supply filter 118. In addition, an inclination with the second liquid supply chamber opening 136 as the uppermost portion (hereinafter referred to as “second liquid supply chamber inclination 138”) is formed on the top surface of the second liquid supply chamber 135.

  As described above, each of the main liquid supply chamber 126, the gas-liquid separator 120, the liquid supply path 137, the supply filter 118, the first liquid supply chamber 134, and the second liquid supply chamber 135 includes the ink discharge port array surface 139. Are set on substantially the same plane. On the other hand, as shown in the cross section along the cutting line IIb-IIb (FIG. 2B), the main liquid supply chamber 126, the liquid supply path 137, the supply filter 118, and the gas-liquid separation unit 120 are It is important to arrange so that they do not overlap each other.

The supply filter 118 is preferably a stainless steel mesh having a filter pore diameter of 1 μm to 10 μm and a filter area of 10 mm ^{2 to} 500 mm ² . By setting the filter hole diameter to 1 μm or more and the filter area to 10 mm ² or more, it is possible to reduce flow path resistance (pressure loss) and facilitate movement of bubbles in the recording head. In order to obtain this effect more reliably, the filter area is more preferably 200 mm ² or more. On the other hand, by setting the filter hole diameter to 10 μm or less, it is possible to reliably prevent dust from flowing into the nozzle. Further, the recording head can be reduced in size by setting the filter area to 500 mm ² or less. In order to more reliably obtain the effects of reducing the channel resistance and preventing the inflow of dust, it is more preferable that the filter pore diameter is 3 μm or more and 8 μm or less.

[2-5] Filling of ink In the recording head of the present invention, the ink for ink jet recording of the present invention is filled in the internal space communicating with the ink discharge port of the line type head. The ink for inkjet recording is preferably filled in at least a portion from the ink discharge port 151 to the common liquid chamber 112 (that is, the nozzle flow path 159 and the common liquid chamber 112) in the internal space.

[3] Inkjet recording apparatus The inkjet recording apparatus of the present invention includes, for example, a recording head for inkjet recording shown in FIG. 2 and an ink storage portion that stores the inkjet recording ink of the present invention supplied to the recording head. . The form of the ink container is not particularly limited. The supply joint 132 of the recording head shown in FIG. 2 and the ink storage unit can be connected using any means known in the art. The discharge joint 133 of the recording head shown in FIG. 2 can be connected to an air discharge unit (not shown).

[3-1] Overall Configuration of Recording Apparatus Other structures of the inkjet recording apparatus are not particularly limited. For example, a so-called full line type ink jet recording apparatus as shown in FIG. 3 can be suitably used. FIG. 3 is a schematic configuration diagram schematically showing the overall configuration of the inkjet recording apparatus 300. An external host device (computer device) 308 is connected to the ink jet recording apparatus 300. The ink jet recording apparatus 300 is configured to record an image by ejecting ink from the recording head 305 based on the recording data input from the computer apparatus 308.

  In the ink jet recording apparatus 300 shown in FIG. 3, a label sheet temporarily attached with a plurality of labels is used as the recording medium 301. The recording medium 301 is set in a state wound in a roll shape. However, in the ink jet recording apparatus of the present invention, any recording medium capable of receiving ink can be used. Non-limiting examples of recording media that can accept ink include paper, cloth, plastic films, metal plates, glass, ceramics, wood, leather, and the like. In one embodiment of the recording method of the present invention, in addition to using the ink jet recording ink of the present invention, as a recording medium, a recording medium having a pore radius peak in the range of 5 to 20 nm (so-called glossy paper). Is used. In this configuration, the glossiness and goodness of the image to be formed are good due to the interaction between the specific particle size distribution of the pigment in the ink for ink jet recording and the pore radius of the recording medium specified in the present invention. It is thought that a good fixability was realized.

  The ink jet recording apparatus 300 includes a transport motor 303, a transport roller 302, a rotary encoder 310, and a roll motor 311 as transport means for transporting the recording medium 301. By driving the transport roller 302 by the transport motor 303, the recording medium 301 can be transported at a constant speed in the direction of arrow A. The rotary encoder 310 can detect the conveyance speed and conveyance amount of the recording medium 301. Further, the recording medium 301 can be rewound in the direction opposite to the arrow A direction by the roll motor 311. The paper detection sensor 304 is a sensor that detects a specific portion of the recording medium 301. In the example of FIG. 3, the leading edge of each label temporarily attached to the label sheet is detected. The recording timing of the image can be determined based on the obtained detection signal.

  The ink jet recording apparatus 300 includes four recording heads 305 and an ink tank 306 corresponding to each of the recording heads 305 in the upper part thereof. The four recording heads are recording heads for ejecting black, cyan, magenta, and yellow ink, respectively.

  The recording head 305 is a so-called line head having a width wider than the maximum width recording width of the recording medium 301 and including a plurality of nozzles capable of ejecting ink. The ink discharge port of the nozzle is opened on the lower surface side of the recording head 305. The recording head 305 is disposed so that its longitudinal direction intersects the direction in which the recording medium 301 is conveyed (perpendicular to the arrow A, the direction perpendicular to the paper surface). A plurality of nozzles are arranged along the longitudinal direction of the recording head 305 to form a nozzle row.

  In the recording apparatus 300, the conveyance roller 302 is driven by the conveyance motor 303, and the recording medium 301 is conveyed at a constant speed in the direction of arrow A by the conveyance roller 302. When a specific portion of the recording medium 301 is detected by the paper detection sensor 304, ink is sequentially ejected from the ink ejection ports of the four recording heads 305 based on the detected position. At this time, the ink is supplied from the ink tank 306 to the recording head 305. As described above, when the recording medium 301 passes under the recording head 305, ink is ejected from the plurality of nozzles of the recording head 305, and an image is recorded on the recording medium 301. The recording head 305, which is a line type head, discharges ink while being fixed at a fixed position. That is, in the full line type recording apparatus as in this example, unlike the so-called serial scan type recording apparatus, the recording head 305 moves in a direction orthogonal to the conveyance direction of the recording medium 301 (see FIG. 3). Do not reciprocate (perpendicular to the page).

  The recording apparatus 300 includes a capping mechanism 307, a blade 309, and the like as a recovery mechanism for performing a recovery operation of the recording head 305.

  The recovery operation is an operation for recovering the recording head 305 so that the recording head 305 exhibits an appropriate ejection performance similar to that in the initial state. Non-limiting examples of the recovery operation include suction recovery, pressure recovery, preliminary discharge, wipe recovery, and the like. The suction recovery is an operation for sucking and removing the ink thickened in the nozzles of the recording head 305 to the capping mechanism 307. The pressure recovery is an operation of pressurizing and discharging the ink thickened in the nozzles of the recording head 305 to the capping mechanism 307. Preliminary ejection is an operation of discharging the ink thickened in the nozzle to the capping mechanism 307 by ejection to stabilize the ink meniscus. Wipe recovery is an operation of wiping the face surface of the recording head with the blade 309 to remove dust and ink adhering to the face surface. These recovery operations can also be implemented in combination.

  The capping mechanism 307 is a mechanism for capping the ink discharge port of each recording head 305 and is disposed below the recording head 305. The recording head 305 and the capping mechanism 307 are configured to be capable of relative movement in the transport direction of the recording medium 301 (the left-right direction in FIG. 3) and the up-down direction. On the other hand, the blade 309 is a member that wipes the face surface of each recording head 305, and is disposed below the recording head 305.

  The suction recovery can be performed by decompressing the inside of the buffer tank (not shown) of the capping mechanism 307 with a tube pump (not shown) while the recording head 305 is capped by the capping mechanism 307. As a result, the thickened ink in the nozzles of the recording head 305 is removed by suction to the capping mechanism 307, and the nozzles are refreshed.

  The pressure recovery can be performed by pressurizing the nozzles of the recording head 305 while the recording head 305 is capped by the capping mechanism 307. As a result, the thickened ink in the nozzle is pressurized and discharged into a cap (not shown) of the capping mechanism 307 to refresh the nozzle.

  Wipe recovery can be performed by driving the blade 309 by a blade motor (not shown) and wiping the face surface of the nozzle of the recording head 305. Preliminary ejection may be further performed after the wipe recovery. Thereby, the face surface of the nozzle is cleaned, and the meniscus at the ink discharge port is adjusted.

  The ink accumulated in the capping mechanism 307 by the above recovery operation is sucked by a tube pump (not shown) and discarded in a waste ink tank (not shown) when it is accumulated to a predetermined amount.

[3-2] Control System Next, control of the ink jet recording apparatus will be described. FIG. 4 is a block configuration diagram of a control system of the ink jet recording apparatus shown in FIG. In addition to a recording mechanism including a recording head, an inkjet recording apparatus includes control system components such as a CPU (Central Processing Unit), a USB interface unit, and a ROM. The CPU 401 executes a program stored in the program ROM 402 and controls each part of the ink jet recording apparatus. The program ROM 402 stores programs and data for controlling the ink jet recording apparatus.

  The recording data output from the computer device 308 is input to the interface controller 403 of the recording device. A command output from the computer device 308 for instructing the number, type, size, and the like of the recording medium (label) is also input to the interface controller 403. In addition to analyzing these commands, the CPU 401 executes arithmetic processing for controlling the entire recording apparatus, such as recording data input, recording operation, and recording medium handling. The arithmetic processing is executed based on a processing program stored in the program ROM 402. The processing program includes a program corresponding to the procedure of the flowchart shown in FIG. A work RAM 404 is used as a working memory for the CPU 401. The EEPROM 405 is a rewritable nonvolatile memory. In the EEPROM 405, the time when the previous recovery operation was performed, the mutual distance between a plurality of recording heads, correction values for finely adjusting the recording position in the transport direction (longitudinal registration), and the like are added to the ink jet recording apparatus. Unique parameters are stored.

  More specifically, after analyzing the input command, the CPU 401 develops the image data of each color component of the recording data in the image memory 406 as a bitmap. Drawing is performed based on this data. Further, the CPU 401 controls the transport motor 303, the roll motor 311, the capping motor 409, the head motor 410, and the pump motor 418 via the input / output circuit 407 and the motor drive unit 408. A capping motor 409 is a motor for driving the capping mechanism 307. The head motor 410 is a motor for moving the recording heads 305K, 305Y, 305M, and 305C. The pump motor 418 is a motor for driving a tube pump (not shown) connected to the capping mechanism 307. The recording heads 305K, 305Y, 305M, and 305C are moved between the capping position, the recording position, and the recovery position. The capping position is a position capped by the capping mechanism 307. The recording position is a position for recording an image. The recovery position is a position for performing a recovery operation.

  When an image is recorded by the recording apparatus, a detection signal from the paper detection sensor 304 is input to the CPU 401 via the input / output circuit 411. When the recording medium 301 is conveyed by the conveyance motor 303, the CPU 401 sequentially reads out image data for each color from the image memory 406 in synchronization with the signal of the rotary encoder 310. The image data for each color is transferred to the corresponding recording head 305K, 305Y, 305M, or 305C via the recording head control circuit 412. The recording heads 305K, 305Y, 305M, and 305C eject ink based on the transferred image data.

  The drive of a pump motor 413 for driving a pump (not shown) is controlled via an input / output circuit 407 and a motor drive unit 408. The operation panel 414 is connected to the CPU 401 via the input / output circuit 415. Further, the environmental temperature and the environmental humidity of the ink jet recording apparatus are detected by a temperature / humidity sensor 416. A detection signal from the temperature / humidity sensor 416 is input to the CPU 401 via the A / D converter 417.

[3-3] Recovery Sequence When the ambient temperature reaches 40 ° C. or higher and the water in the ink evaporates, the ink sticks easily in the recording head 305. Accordingly, it is preferable to implement a recovery sequence for recovering the face surface of the recording head 305 when the capping mechanism 307 is away from the recording head 305 and the water in the ink is evaporated.

  FIG. 5 is a flowchart showing the steps of the recovery sequence of the recording head 305. The recovery sequence is activated on condition that the recording head 305 is in the cap open state released from the capping mechanism 307 (step S501). When the recovery sequence is activated, the environmental temperature and the environmental humidity of the ink jet recording apparatus are acquired (detected) by the temperature / humidity sensor 416 (step S502). Then, on condition that the environmental temperature is 40 ° C. or higher, the environmental humidity is 70% RH or lower, and the elapsed time from the previous suction recovery is 1 hour or longer (steps S503 and S504), A recovery process is performed (step S505). Specifically, pressure recovery or preliminary ejection for refreshing the ink in the nozzle and wipe recovery for wiping and cleaning the face surface are performed (step S505). Note that the elapsed time in step S504 is reset when suction recovery is performed.

[3-4] Recording Head of Another Configuration The present invention can also be applied to a so-called serial scan type inkjet recording apparatus. In this case, for example, a serial type head that has a width smaller than the maximum width recording width of the recording medium 301 and ejects ink while moving in a direction intersecting (for example, orthogonal) with the conveyance direction of the recording medium 301 is used. Can be used. When such a serial type head is used, for example, an ink tank as shown in FIG. 6 can be used as the ink containing portion.

  The ink tank 230 is a liquid storage container in which a liquid chamber (ink chamber 231) for storing ink is formed. The ink chamber 231 is a closed space that can communicate with the outside only at the joint portion 232. The ink tank 230 is configured to be detachable from the recording head. The ink tank 230 is provided in the upper part of the recording head. The ink chamber 231 is formed of a flexible member. The ink chamber 231 includes a spring 233-1 for generating negative pressure and a pressure plate 233-2 connected to the spring 233-1. The spring 233-1 urges the ink chamber 231 from the inside to the outside via the pressure plate 233-2, and expands the internal space of the ink chamber 231. That is, the spring 233-1 generates a predetermined negative pressure inside the ink chamber 231. The spring 233-1, the pressure plate 233-2, and the ink chamber 231 constitute a negative pressure generating unit 233 as a unit. The joint portion 232 is provided with a non-woven filter 234.

  FIG. 7 is an enlarged cross-sectional view of the serial type recording head 220. The recording head 220 includes an energy generation element (not shown) such as an electrothermal conversion element (ink ejection heater). The ink I in the ink chamber 221 (liquid in the liquid chamber) is discharged from the discharge port 220A by the energy generating element. In the ink chamber 221, air (gas) is present together with the ink I. Therefore, in the ink chamber 221, there are an ink storage part (liquid storage part) in which the ink I is stored and an air storage part (gas storage part) in which air (gas) is stored.

  An ink supply unit 222 for communicating the ink chamber 221 of the recording head 220 with the ink chamber 231 of the ink tank 230 is provided above the ink chamber 221. On average, the ink supply unit 222 has a width of about 10 mm. A filter member 223 is provided at the opening of the ink supply unit 222. The filter member 223 may have a mesh structure in which metal fibers such as SUS are woven. Since the filter member 223 has fine eyes, it becomes difficult for dust to enter the recording head 220 from the outside.

  The lower surface of the filter member 223 is pressed against an ink holding member 224 that can hold ink. 8A is an enlarged perspective view of the ink holding member shown in FIG. 7, and FIG. 8B is a cross-sectional view of the ink holding member shown in FIG. 8A taken along line VIIIb-VIIIb. As shown in FIGS. 8A and 8B, the ink holding member 224 has a plurality of flow paths 224A having a circular cross section. Each flow path 224A has a diameter of about 1.0 mm.

  Further, as shown in FIG. 7, an opening 225 is provided in the upper part of the ink chamber 221. The opening 225 is provided with a filter 226. The opening 225 is configured to be connectable to a transfer unit (not shown) that is an external flow path. This transfer part is a flow path capable of transferring liquid and / or gas. The opening 225 allows the ink I and / or gas in the ink chamber 221 to flow out, or allows liquid (such as ink) and / or gas outside the recording head 220 to flow into the ink chamber 221. It is configured. That is, the opening 225 is formed so that not only the liquid can flow out and flow in alone, but also the gas can flow out and flow in with the liquid.

  The ink tank 230 shown in FIG. 6 and the recording head 220 shown in 214 are directly connected by connecting the joint part 232 of the ink tank 230 shown in FIG. 6 and the ink supply part 222 of the recording head 220 shown in FIG. Connected to. At this time, the filter 234 of the ink tank 230 shown in FIG. 6 and the filter member 223 of the recording head 220 shown in FIG. 7 are in pressure contact with each other from above and below. The connecting portion between the ink tank and the recording head formed in this manner is surrounded by a rubber elastic cap member to maintain hermeticity. The structure in which the recording head and the ink tank are directly connected as described above is preferable in that the ink supply path (liquid supply path) between them can be extremely shortened.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to the configurations of the following examples. Unless otherwise specified, “part” and “%” in the following description mean “part by mass” and “% by mass”.

[Synthesis Example 1: Synthesis of (meth) acrylic ester random copolymer 1]
1000 parts of methyl ethyl ketone (MEK) was introduced into a reaction vessel equipped with a stirrer, a dropping device, a temperature sensor, a reflux device, and a nitrogen introduction device on the reflux device. While stirring MEK, the inside of the reaction vessel was replaced with nitrogen. After heating MEK in the reaction vessel to 80 ° C., 63 parts 2-hydroxyethyl methacrylate (HEMA), 128 parts methacrylic acid (MAA), 417 parts styrene (Sty), 201 parts from a dropping device. Benzyl methacrylate (BnMA), 25 parts glycidyl methacrylate (GMA), 33 parts polymerization degree modifier (Blenmer TGL (manufactured by NOF Corporation)), and 67 parts t-butyl peroxy-2-ethylhexanoate 67 parts of the mixture was added dropwise over 4 hours. After completion of the dropwise addition, the reaction is further continued at 80 ° C. for 10 hours, and a (meth) acrylic acid ester system having an acid value of 100 mgKOH / g, a glass transition point (Tg) of 89 ° C., and a weight average molecular weight (Mw) of 8000. A solution of random copolymer (A-1) was obtained. The resin content in the solution was 45.4%.

[Synthesis Examples 2 to 5: Synthesis of (meth) acrylic acid ester random copolymers 2 to 5]
Except having changed the compounding quantity of the monomer in the dripping mixture as shown in Table 1, the procedure of the synthesis example 1 was repeated and the (meth) acrylic acid ester random copolymers 2-5 were obtained. . The acid values of the obtained (meth) acrylic acid ester random copolymers 2 to 5 are shown in Table 1. The (meth) acrylic acid ester-based random copolymers 2 to 3 are resins for preparing the ink jet recording inks of Examples. On the other hand, the (meth) acrylic acid ester-based random copolymers 4 to 5 are resins for preparing the ink jet recording ink of the comparative example.

[Synthesis Example 6: Preparation of resin dispersed pigment 1]
A (meth) acrylic ester random copolymer 1 solution (resin content: 45.4%), 25% aqueous potassium hydroxide solution, water and 1000 parts of carbon black were introduced into a mixing tank equipped with a cooling jacket. And stirred and mixed to obtain a mixture. Here, the introduction amount of the solution of the (meth) acrylic acid ester random copolymer 1 was such that the resin content was 40% of the carbon black. The amount of the 25% potassium hydroxide aqueous solution introduced was such that the introduced (meth) acrylate random copolymer 1 was neutralized 100%. In addition, the amount of water introduced was an amount necessary to make the concentration of nonvolatile components in the obtained mixed liquid 27%. The obtained mixed liquid was transferred into a dispersing apparatus filled with zirconia beads having a diameter of 0.3 mm, and circulated for 4 hours while maintaining the temperature of the mixed liquid at 40 ° C. or lower to obtain a dispersion.

  The dispersion liquid was taken out from the mixing tank. Subsequently, the mixing tank and the flow path of the dispersion apparatus were washed with 10,000 parts of water, and the obtained washing liquid was combined with the dispersion liquid to obtain a diluted dispersion liquid. The total amount of MEK and a part of water were removed from the diluted dispersion by distillation to obtain a concentrated dispersion. The resulting concentrated dispersion was cooled to room temperature. To the concentrated dispersion at room temperature, 2% hydrochloric acid was added dropwise with stirring to adjust the pH of the concentrated dispersion to 4.5. The obtained concentrated dispersion was filtered with a Nutsche filter, and the resulting solid was washed with water. Water was added to the obtained solid (cake) and redispersed using a dispersion stirrer. A 25% aqueous potassium hydroxide solution was added to the redispersion to adjust the pH of the redispersion to 9.5. The coarse particles were then removed from the redispersion by centrifugation at 6000 G for 30 minutes. Water was added to the resin-dispersed pigment from which coarse particles had been removed so that the nonvolatile content was 20% to obtain a resin-dispersed pigment dispersion. Further, water was added to the resin-dispersed pigment dispersion so that the resin-dispersed pigment concentration was about 14% to obtain Pigment Dispersion 1 used for preparing ink for inkjet recording.

[Synthesis Examples 7 to 10: Preparation of resin dispersed pigments 2 to 5]
The procedure of Synthesis Example 6 was repeated except that the solution of (meth) acrylate random copolymer 2-5 was used instead of the solution of (meth) acrylic ester random copolymer 1, Pigment dispersions 2 to 5 were obtained. In all of the pigment dispersions 2 to 5, the resin dispersion pigment concentration was adjusted to 14%.

[Example 1: Preparation of ink for inkjet recording]
21.4 parts of Pigment Dispersion 1 (pigment concentration about 14%) were added to the container. Subsequently, 5.0 parts phthalocyanine compound 1 (concentration 10%), 27.5 parts ethylene urea 40% aqueous solution, 7 parts glycerin 7 parts, 2 parts triethylene glycol, 3.1 parts bis (2 -Hydroxyethyl) sulfone 65% aqueous solution was added. Furthermore, 0.5 parts of acetylenol E100 (ethylene oxide adduct of 2,4,7,9-tetramethyl-5-decyne-4,7-diol, manufactured by Kawaken Fine Chemical Co., Ltd.) and NIKKOL BC-20 (polyoxy) 1.0 part of ethylene (20) cetyl ether, manufactured by Nikko Chemicals Co., Ltd. was added. Finally, pure water (ion exchange water) was added to make 100 parts as a whole. The resulting mixture was stirred with a propeller stirrer over 30 minutes. The obtained mixed liquid was filtered with a filter having a pore size of 3.0 μm to obtain black ink jet recording ink. The resulting inkjet recording ink contained 11 parts ethylene urea and 2 parts bis (2-hydroxyethyl) sulfone. Table 2 shows the ink composition and characteristics (concentration of the resin-dispersed pigment, the concentration of the phthalocyanine compound, and the ratio of the resin-dispersed pigment and the phthalocyanine compound) of the obtained ink for inkjet recording.

[Examples 2 to 11 and Comparative Examples 1 to 6: Preparation of ink for inkjet recording]
Except that the ink composition was changed as shown in Tables 2 and 3, the procedure of Example 1 was repeated to obtain ink jet recording inks of Examples 2 to 11 and Comparative Examples 1 to 6. The characteristics of the obtained ink for ink jet recording are shown in Tables 2 and 3.

(Evaluation methods and standards)
Inkjet recording of Examples 1 to 11 and Comparative Examples 1 to 6 using a thermal inkjet recording apparatus (LX-P5500, manufactured by the present applicant) having the nozzle shown in FIG. 1 and the recording head shown in FIG. The ink for evaluation was evaluated. Table 4 shows the specifications of the recording head of the ink jet recording apparatus used.

<Discharge stability>
Ink jet recording inks of Examples 1 to 11 and Comparative Examples 1 to 6 were filled into the above-described ink jet recording apparatus. In an environment having a temperature of 15 ° C. and a humidity of 10% RH, one drop of ink was ejected from each nozzle, and one line was recorded on the mat label (manufactured by the present applicant). When recording, the head exposure time from preliminary ejection to recording was changed. The deviation and variation of the recorded lines and the interruption of the recorded lines due to non-ejection of ink from the recording head were visually evaluated. The maximum value of the head exposure time that allows normal recording was adopted as the evaluation value of ejection stability. The evaluation values of the discharge stability are shown in Tables 2 and 3.

  As can be seen from Tables 2 and 3, the inkjet recording inks of Examples 1 to 11 according to the present invention exhibited good ejection stability. Specifically, the maximum value of the head exposure time that allows normal recording with the ink jet recording inks of Examples 1 to 11 was 5 seconds or longer than that of the ink jet recording ink of Comparative Example 1 that did not contain a phthalocyanine compound.

  Moreover, the inkjet recording inks of Comparative Examples 2 to 6 exhibited lower ejection stability than the inkjet recording inks of Examples 1 to 9. In the inkjet recording ink of Comparative Example 2, since the acid value of the (meth) acrylic ester random copolymer used as the dispersant was low, the pigment was not sufficiently dispersed. In the ink for inkjet recording of Comparative Example 3, since the acid value of the (meth) acrylic acid ester random copolymer used as the dispersant was too high, the ejection stability was lowered due to thickening of the ink. In the inkjet recording ink of Comparative Example 4, the discharge stability was lowered due to the low dispersibility of the phthalocyanine compound not satisfying the formula (I). In the inkjet recording ink of Comparative Example 5, since the amount of the phthalocyanine compound added to the resin-dispersed pigment was too small, the ejection stability was lowered. In the inkjet recording ink of Comparative Example 6, since the amount of the phthalocyanine compound added to the resin-dispersed pigment was too large, agglomeration due to excessive dispersion occurred and ejection stability was lowered.

  As explained above, the resin-dispersed pigment containing carbon black dispersed by a (meth) acrylic acid ester-based random copolymer having an acid value of 100 mgKOH / g or more and 160 mgKOH / g or less, and the general formula (I) By using an ink for ink jet recording having a mass ratio of the resin-dispersed pigment and the phthalocyanine compound of 1.5: 1 to 6: 1, a good ejection stability can be obtained. I understood.

152 Electrothermal converter (heater)
220, 305 Recording head 230, 306 Ink tank 300 Recording device I Ink

Claims (6)

An inkjet recording ink containing at least a pigment, a phthalocyanine compound, water, and a water-soluble compound,
The pigment is a resin-dispersed pigment containing carbon black dispersed by a (meth) acrylic acid ester-based random copolymer having an acid value of 100 mgKOH / g or more and 160 mgKOH / g or less,
The phthalocyanine compound has the general formula (I)
(In the formula, l and m each represent an integer of 0 to 5, n represents an integer of 1 to 5, and l + m + n = 2 to 5)
An ink for ink jet recording, wherein the mass ratio of the resin-dispersed pigment and the phthalocyanine compound is 1.5: 1 to 6: 1.   The (meth) acrylic acid ester-based random copolymer is a random copolymer of 2-hydroxyethyl methacrylate, methacrylic acid, styrene, benzyl methacrylate, and glycidyl methacrylate. The ink for inkjet recording according to claim 1.   The ink for inkjet recording according to claim 1 or 2, wherein a mass ratio of the (meth) acrylic ester random copolymer to the carbon black is in a range of 0.2 to 1.0. . An inkjet recording method for performing recording by ejecting ink from a plurality of nozzles forming a nozzle row by a thermal method, wherein each of the nozzles has an opening area of 100 μm ² or more and 350 μm ² or less, and the ink is claimed. 4. An ink jet recording method, which is the ink for ink jet recording according to any one of 1 to 3.   5. The ink jet recording method according to claim 4, wherein the number of the nozzles forming the nozzle row is 1200 or more, and the length of the nozzle row is 5.08 cm (2 inches) or more. An ink jet recording apparatus provided with an ink containing portion and a recording head,
The ink container contains the ink for ink jet recording according to any one of 1 to 3,
The ink-jet recording apparatus, wherein the recording head ejects the ink-jet recording ink supplied from the ink container from a nozzle by a thermal method.